Cannabinoid conversion in cannabis extracts

ABSTRACT

The present invention is a process for producing various types of  cannabis  extract from harvested  cannabis . A quantity of harvested  cannabis , which typically includes the inflorescence, floral leaves, and small stems of a flowering  cannabis  plants, is pre-frozen. The harvested  cannabis  is first subjected to cryogenic grinding to produce pulverized  cannabis . The pulverized  cannabis  is then subjected to alcohol extraction to produce an initial  cannabis  extract, which can be subjected to one of several forms of further processing according to the desired chemical profile of the final product. The initial  cannabis  extract may then be subjected to chemical processing that promote the conversion of THCA to Δ9 THC; the conversion of THCVA to THCV; the conversion of THCA to cannabinol (“CBN”); or the conversion of THCA to Δ8-THC.

This application is a continuation of U.S. patent application Ser. No. 16/365,614, entitled “Producing Cannabis Extracts via Selective Decarboxylation” filed on Mar. 26, 2019, now U.S. Pat. No. 10,471,113, issued Nov. 12, 2019, which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

The cannabis plant (Cannabis sativa L.) (“cannabis”) has a long history of being used for medicinal and recreational purposes. Cannabis plant material contains a variety of chemical compounds, including those responsible for the “high” associated with cannabis consumption as well as other physiological effects. Among the compounds present in cannabis are tetrahydrocannabinolic acid (“THCA”) and tetrahydrocannabivaric acid (“THCVA”). While THCA and THCVA themselves produce few physiological effects when directly ingested, exposing THCA and THCVA to high temperatures, such as those produced when cannabis burns during smoking, causes those compounds to undergo decarboxylation reactions to form psychoactive or other physiologically active compounds. THCA, in particular, is well-known for its conversion via decarboxylation to Δ9-tetrahydrocannabinol (“Δ9-THC”), which is psychoactive. Upon heating, THCVA undergoes a similar decarboxylation reaction to form tetrahydrocannabivarin (“THCV”), which has appetite-suppressing effects.

As of February 2019, ten U.S. states have legalized the recreational use of cannabis, and thirty-two U.S. states have legalized the use of cannabis for medicinal purposes. As the state-level legalization of cannabis has expanded, so has the production of cannabis-derived products. Cannabis extracts (sometimes known as “cannabis oils”) have emerged as an important category of cannabis-derived product. Cannabis extracts are produced by subjecting cannabis to an extraction process, wherein solvents are used to dissolve (“extract”) chemical compounds from harvested cannabis plant material.

In existing methods of making cannabis extracts, harvested cannabis or cannabis extract may be heated in an oven to achieve the decarboxylation of compounds, such as THCA and THCVA, to form psychoactive or physiologically active compounds, such as Δ9-THC and THCV. A major drawback of oven-based decarboxylation is the tendency to cause the loss of desirable volatile compounds, such as caryophyllene and other terpenes, through evaporation or heat-induced chemical reactions. Accordingly, a process is needed to enable a greater degree of control over the decarboxylation of cannabis extracts.

SUMMARY OF THE INVENTION

The present invention is a process for producing various types of cannabis extract from harvested cannabis. A quantity of harvested cannabis, which typically includes the inflorescence, floral leaves, and small stems of a flowering cannabis plants, is pre-frozen. The harvested cannabis is first subjected to cryogenic grinding to produce pulverized cannabis. The pulverized cannabis is then subjected to alcohol extraction to produce an initial cannabis extract, which can be subjected to one of several forms of further processing according to the desired chemical profile of the final product. The initial cannabis extract may then be subjected to chemical processing that promote the conversion of THCA to Δ9-THC; the conversion of THCVA to THCV; the conversion of THCA to cannabinol (“CBN”); or the conversion of THCA to Δ8-tetrahydrocannabinol (“Δ8-THC”).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram showing the steps for converting harvested cannabis to pulverized cannabis through cryogenic grinding;

FIG. 2 is a flow diagram showing the steps for converting pulverized cannabis to an initial cannabis extract using alcohol extraction;

FIG. 3 is a flow diagram showing the steps for producing Δ9-THC and THCV via decarboxylation of an initial cannabis extract;

FIG. 4 is a flow diagram showing the steps for producing cannabinol via decarboxylation of an initial cannabis extract; and

FIG. 5 is a flow diagram showing the steps for producing Δ8-THC via decarboxylation of a cannabis extract containing Δ9-THC.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a process that includes several stages, which are described below as Stages 1-2, 3A-3C, and 4. Where the process refers to the use of “alcohol,” a solution containing at least 99% ethanol by volume or at least 99% isopropyl alcohol by volume is preferred although concentrations as low as about 95% alcohol can be used Specifically, “ethyl alcohol 200 proof” or “99.9% isopropyl alcohol” supplied by Green Wood Cleaning Products, Inc., of Hollister, Calif., may be used.

Stage 1: Cryogenic Grinding

Referring to FIG. 1, cryogenic grinding is used to convert a quantity of harvested cannabis 10 into pulverized cannabis 14. The harvested cannabis 10, which may be fresh or cured, should be pre-frozen (step 11) at a temperature of about −29° C. (−20° F.) prior to processing. Cryogenic grinding should take place at an ambient temperature of 0-10° C. (32-50° F.). An ambient temperature of 0° C. (32° F.) is preferable for minimizing the loss of compounds from the harvested cannabis through evaporation or chemical reactions that would occur at higher temperatures, but acceptable results can still be obtained when the ambient temperature is as high as 10° C. (50° F.). In practice, it is advisable to perform cryogenic grinding in a cold room or a walk-in freezer.

When pre-freezing is complete, the harvested cannabis is separated into batches (step 12) weighing approximately 450 g (1.0 lb) each. For each batch, the harvested cannabis is placed into a plastic bag capable of accommodating a volume of approximately 15 cm×48 cm×20 cm (6 in.×19 in.×8 in.). A Reynolds® turkey-size oven cooking bag may be used. The bag is then sealed; sealing may be accomplished by tying the open end of the bag into a knot or with a suitable fastener, such as twist tie. The batches of harvested cannabis are then processed in a tumbling apparatus (step 13).

The tumbling apparatus is a horizontally oriented cylindrical drum that is capable of rotating about its own axis. The drum should be capable of performing approximately 40 rotations per minute (rpm). The drum may have a diameter of approximately 60 cm (24 in.) and a length of approximately 91 cm (36 in.). A Triminator® Dry cannabis-trimming machine supplied by Dana Mosman of Boulder, Colo., may serve as the tumbling apparatus.

Five bags of harvested cannabis are placed into the tumbling apparatus. Approximately 680 g (1.5 lb) of dry ice (i.e., solid carbon dioxide) is placed into the tumbling apparatus along with the bags of harvested cannabis. The dry ice may be in the form of uniformly sized cylindrical pieces that are approximately 0.64 cm (0.25 in.) in diameter and approximately 5.0 cm (2.0 in) in height. Dry-ice “nuggets” supplied by Praxair Technology, Inc., of Danbury, Conn., may be used.

The bags of harvested cannabis are tumbled at approximately 40 rpm for about 10 minutes. The appropriate rotational speed can be achieved with a Triminator® Dry cannabis-trimming machine or with a rheostat controlling the motor speed of a dedicated tumbler. During the tumbling process, the agitation of the harvested cannabis within each bag, in conjunction with the physical impacts of the dry ice against the bag, pulverize the harvested cannabis to a fine powder, thereby producing pulverized cannabis 14.

It will be appreciated that the amount of cannabis that can be processed by the tumbling apparatus depends on the size of the tumbling apparatus. The equipment can readily be scaled up for larger amounts of cannabis.

Stage 2: Alcohol Extraction

Referring to FIG. 2, alcohol extraction is used to separate the compounds present within the pulverized cannabis from solid plant matter. In preparation for alcohol extraction, the bags of pulverized cannabis 14 are removed from the tumbling apparatus and transferred into filter bags (step 21). Each batch of cannabis is transferred from the plastic bag used during cryogenic grinding to a filter bag having a pore diameter of about 220 μm. The filter bag should be sufficiently large to accommodate the pulverized cannabis without deliberate packing. A Bubble Bags® filter bag with a nominal capacity of 3.78 L (1 gal) and a pore diameter of 220 μm supplied by Fresh Headies Internet Sales Ltd. of Vancouver, Canada, may be used. Transfer of the pulverized cannabis is preferably performed at the same ambient temperature as cryogenic grinding to prevent premature warming of the pulverized cannabis.

Two filter-bags of pulverized cannabis are placed into an extraction apparatus for alcohol extraction (step 22). The extraction apparatus is an upright cylindrical drum that is capable of rotating about its own axis. The drum can have a diameter of approximately 38 cm (15 in.) and height of approximately 38 cm (15 in.) and should be capable rotating at 40 rpm. The extraction apparatus is prefilled with approximately 40 L (10 gal) of alcohol. The alcohol should completely immerse the filter bags without a risk of overflowing from the extraction apparatus. The alcohol is preferably pre-chilled to −20° C. to −30° C., preferably to −25° C., to minimize any undesirable extraction of chlorophyll and lipid material from the pulverized cannabis. The extraction process, however, will produce acceptable results with an alcohol temperature as high as 0° C. (32° F.). To maintain chilling of the alcohol during the extraction process, the extraction apparatus may be placed in a chest freezer or cold room.

Once immersed, the drum of the extraction apparatus is rotated at approximately 40 rpm for 10 minutes, during which compounds from the pulverized cannabis dissolve into the alcohol. The alcohol normally takes on a bright-green color as extraction proceeds. The alcohol is then poured from the extraction apparatus for collection (step 23). The filter bags, which remain in the extraction apparatus, are subjected to centrifugation at 200 g to spin out any residual alcohol that remains within the filter bags (step 24). The filter bags may be manually rearranged within the extraction apparatus prior to centrifugation to ensure adequate balance. The residual alcohol is combined with the alcohol obtained by pouring.

The alcohol is then passed through a stainless-steel mesh filter with a pore diameter of about 32 μm (step 25), and the filtrate (the “first-pass filtrate”) is collected. The first-pass filtrate is again passed through the same filter (step 26), and the resulting twice-filtered liquid (the “second-pass filtrate”) is collected. An 8-inch diameter test sieve with a pore opening size of 32 μm (No. 450) supplied by W.S. Tyler (a division of Haver Tyler, Inc.) of Mentor, Ohio, may be used as the filter. The second-stage filtrate is subjected to rotary evaporation at about 40° C. (104° F.) at a reduced pressure of about 5332 Pa (40 Torr or 0.05 atm) until substantially all of the alcohol is removed (step 27). The liquid that remains is the initial cannabis extract 28, which may be stored or subjected to one of the further processing steps designated as Stages 3A-3C below. For every two filter-bags of pulverized cannabis, the extraction process produces approximately 300 ml of initial cannabis extract. The initial cannabis extract is preferably stored at 0° C. (32° F.) while awaiting further processing.

A CUP-30 Centrifuge Utility Platform Alcohol Extraction System (the “CUP-30 system”) made by Delta Separations LLC of Santa Rosa, Calif., may serve as the extraction apparatus. The ratio of alcohol to pulverized cannabis described above (i.e., approximately 40 L of alcohol for every 2 filter-bags of pulverized cannabis) may be scaled up to fully use the processing capacity of the CUP-30 system.

Stage 3A: Conversion of Tetrahydrocannabinolic Acid in the Initial Cannabis Extract to Delta-9-Tetrahydrocannabinol

Referring to FIG. 3, a first diluted solution 31 is produced by diluting the initial cannabis extract 28 to 120% of its initial volume using alcohol. For example, 80 ml of initial cannabis extract 28 should be combined with enough alcohol to produce 100 ml of the first diluted solution. The volume of the first diluted solution is further increased by 3%-5% through the addition of water to produce a second diluted solution (step 32). For example, 100 ml of the first diluted solution may be combined with enough water to make 103-105 ml of the second diluted solution. The presence of the water within the second diluted solution inhibits the undesirable formation of cannabinol (“CBN”) as well as the degradation of terpenes and cannabinoids.

The second diluted solution is refluxed at 80-100° C. for 1-3 hours, preferably 80° C. for 2 hours, to promote the decarboxylation of THCA to form Δ9-THC (step 33). Acceptable results can be obtained by refluxing at 100° C. for 1 hour, and the higher temperature may result in an increase in the undesirable formation of CBN. Refluxing is performed in a flask attached to a cold condenser whose temperature is −30° C. to −40° C., preferably −40° C. The cold condenser may be cooled by propylene glycol circulated by an external chiller. Following refluxing, the second diluted solution is subjected to rotary evaporation (step 35) until substantially all of the diluent is removed. The liquid that remains is a refined cannabis extract enriched in Δ9-THC 36.

Refluxing may be used to process the initial cannabis extract in batches of 300 ml. Batch sizes may be adjusted according to the capacity of the refluxing apparatus.

Stage 3B: Conversion of Tetrahydrocannabivaric Acid in the Initial Cannabis Extract to Tetrahydrocannabivarin

Referring to FIG. 3, the initial cannabis extract 28 is converted to a first diluted solution and then a second diluted solution (steps 31 and 32) as in Stage 3A above. The second diluted solution is refluxed for 1-2 hours, preferably 1.5 hours, at a temperature of 120° C. to promote the decarboxylation of THCVA to form THCV (step 34). Refluxing is performed in a flask attached to a cold condenser whose temperature is −30° C. to −40° C. The cold condenser may be chilled as in Stage 3A above. Following refluxing, the second diluted solution is subjected to rotary evaporation (step 35) until substantially all diluent is removed. The liquid that remains is a refined cannabis extract that is enriched in THCV 37.

Stage 3C: Increasing Cannabinol Content of Initial Cannabis Extract

Referring to FIG. 4, the initial cannabis extract 28 is diluted with alcohol to a concentration of 80% by volume to produce a diluted solution 41. For example, 80 ml of initial cannabis extract 28 should be combined with enough alcohol to produce 100 ml of the diluted solution. The diluted solution is refluxed at 180° C. for 1-3 hours, preferably 2 hours, to promote the formation of cannabinol (step 42). Following refluxing, the diluted solution is subjected to rotary evaporation (step 43) until substantially all alcohol is removed. The liquid that remains is a refined cannabis extract that is enriched in cannabinol 44.

Stage 4: Increasing Δ8-Tetrahydrocannabinol Content of the Initial Cannabis Extract

Referring to FIG. 4, the initial cannabis extract 28 is converted to a refined cannabis extract enriched in Δ9-THC 36 according to the steps in Stage 3A above.

Referring to FIG. 5, the volume of the refined cannabis extract 36 is then increased by 7.5%-15%, preferably 10%, by the addition of powdered bleaching clay (step 51). T-41 Canna Bleach supplied by Carbon Chemistry Ltd. of Watkins, Colo., may be used. The volume of refined cannabis extract is then increased by another 7.5%-15%, preferably 10%, by the addition of activated charcoal in powdered form (step 52). The volume of powdered bleaching clay added should be identical to the volume of activated charcoal added. Carbon Powder A supplied by Summit Research of Scotts Valley, Calif., may be used. For example, 100 ml of refined cannabis extract may be combined with 7.5 cm³ of specialty bleaching clay and 7.5 cm³ of activated charcoal to produce a mixture having a final volume of 115 ml.

The resulting mixture is subjected to distillation using a short-path distillation apparatus (the “distillation apparatus”). The distillation apparatus is composed of a feed flask, which contains the mixture. The feed flask is placed on a combination hotplate-magnetic stirrer, which allows a liquid within the feed flask to be simultaneously heated and agitated by a stir bar. The feed flask is attached to a condenser, which, in turn, is preferably attached to a “triple cow”-style distillation receiver with a connection point for a vacuum source. Two flasks are connected to the distillation receiver, the first for collecting undesirable distillates (the “waste flask”); and the second for collecting desirable distillates (the “collection flask”). Unneeded connections on the distillation apparatus should be sealed with stoppers. The temperature of the condenser is maintained at 21-23° C. (70-74° F.) by the circulation of water. A distillation receiver (Mfr. No. CG-1276-01) supplied by Thomas Scientific LLC of Swedesboro, N.J., may be used.

The mixture is placed into the feed flask, and the waste flask is placed in a position to receive distillate. The distillation apparatus is connected to a vacuum source, and the pressure within the distillation apparatus is reduced to approximately 66.7 Pa (500 mTorr or 6.7×10⁻⁴ atm). The mixture is gradually heated to 140° C. while being agitated by the stir bar (step 53). It is important to ensure that the mixture does not foam (or “muffin”) during distillation. Uncontrolled foam may expand to reach and contaminate the condenser, making the distillate unsuitable for use. To minimize foaming, it is advisable to set the stir bar to an initial speed of 400 rpm. The mixture is then gradually heated at a rate of approximately 15° C. per minute, and speed of the stir bar increased at a rate of approximately 50 rpm per minute, until the mixture reaches 140° C. and the stir bar reaches 900 rpm. Any distillate that incidentally emerges during the initial heating process is collected in the waste flask.

Once the mixture reaches 140° C., the distillate should take on a bluish color as azulene and derivatives thereof begin to distill from the mixture. Heating of the mixture should continue at the rate of approximately 1° C. per minute until the mixture reaches 157° C. During the heating period, bluish distillate continues to distill from the mixture and is collected in the waste flask (step 54). The temperature of the mixture is maintained at 157° C. until the condensing distillate is colorless, at which point all azulene and derivatives thereof have been removed from the mixture.

The colorless distillate is collected in the collection flask, which should be rotated into position as soon as bluish distillate stops appearing. The temperature of the mixture is further increased at the rate of approximately 1° C. per minute until it reaches 175° C. The distillate, which now contains Δ8-THC, continues to be collected in the collection flask during this period (step 55). The mixture is maintained at a temperature of 175° C. until substantially all of the liquid in the feed flask is depleted. The mixture is then heated to 220° C., and distillate is collected until no further distillate is produced (step 56). The final heating to 220° C. promotes the full conversion of liquid remaining in the feed flask to the vapor phase. The distillate is a refined cannabis extract enriched in Δ8-THC 57.

The refined cannabis extract enriched in Δ8-THC 57 should be colorless. If the distillate in the collection flask has a noticeable color, such as amber or teal, the distillate should be treated as the cannabis extract enriched in Δ9-THC 36 and subjected to a second round of processing according to steps 51-56.

Referring to FIG. 4, the initial cannabis extract 28 is diluted with alcohol to a concentration of 90% by volume to produce a diluted solution 41. For example, 90 ml of initial cannabis extract 30 should be combined with enough alcohol to produce 100 ml of the diluted solution. The magnetic stirrer is turned on to about 500 rpm. The diluted solution is then refluxed at between 180° C.-220° C. for 1-3 hours, preferably 2 hours, to promote the formation of cannabinol (step 42). Following refluxing, the diluted solution is subjected to rotary evaporation (step 43) until substantially all alcohol is removed. The liquid that remains is a refined cannabis extract that is enriched in cannabinol 44.

Referring to FIG. 4, the initial cannabis extract 28 is converted to a refined cannabis extract enriched in CBN 44 according to the steps in Stage 3C above.

The following claims are thus to be understood to include what is specifically illustrated and described above; what is conceptually equivalent; and what can be obviously substituted. Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope of the invention. The illustrated embodiment has been set forth only for the purposes of example and should not be taken as limiting the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein. 

What is claimed is:
 1. A method of producing a refined cannabis extract, the method comprising the steps of: converting a quantity of harvested cannabis to pulverized cannabis using cryogenic grinding; extracting the pulverized cannabis with alcohol to yield an initial cannabis extract; and subjecting the initial cannabis extract to a decarboxylation process. 2-3. (canceled)
 4. The method of claim 1, wherein the decarboxylation process comprises the steps of: adding a quantity of alcohol to the initial cannabis extract to produce a diluted solution; and refluxing the diluted solution at a temperature of about 180° C. for a period of about 1-3 hours.
 5. (canceled)
 6. A refined cannabis extract prepared by a process comprising the steps of: converting a quantity of harvested cannabis to pulverized cannabis using cryogenic grinding; extracting the pulverized cannabis with alcohol to yield an initial cannabis extract; and subjecting the initial cannabis extract to a decarboxylation process.
 7. The refined cannabis extract of claim 6, wherein the decarboxylation process comprises the steps of: adding a quantity of alcohol to the initial cannabis extract to produce a first diluted solution; adding a quantity of water to the first diluted solution to produce a second diluted solution; and refluxing the second diluted solution at a temperature of about 80-100° C. for a period of about 1-3 hours.
 8. The refined cannabis extract of claim 6, wherein the decarboxylation process comprises the steps of: adding a quantity of alcohol to the initial cannabis extract to produce a first diluted solution; adding a quantity of water to the first diluted solution to produce a second diluted solution; and refluxing the second diluted solution at a temperature of about 120° C. for a period of about 1-2 hours.
 9. The refined cannabis extract of claim 6, wherein the decarboxylation process comprises the steps of: adding a quantity of alcohol to the initial cannabis extract to produce a diluted solution; and refluxing the diluted solution at a temperature of about 180° C. for a period of about 1-3 hours.
 10. The refined cannabis extract of claim 7, wherein the decarboxylation process further comprises the steps of: after refluxing, adding a quantity of bleaching clay and a quantity of activated charcoal to the second diluted solution to produce a mixture; and distilling the mixture at a temperature of about 157-220° C.
 11. A method of producing a refined, decarboxylated cannabis extract, the method comprising the steps of: a) freezing a quantity of cannabis to make frozen cannabis; b) grinding the frozen cannabis at cryogenic temperatures to produce pulverized cannabis; c) extracting the pulverized cannabis with a quantity of alcohol; d) separating the alcohol from the pulverized cannabis to obtain an initial cannabis extract; e) diluting the initial cannabis extract with a quantity of alcohol to produce a diluted initial cannabis extract; and f) refluxing the diluted initial cannabis extract at a temperature of about 180° C. for a period of about 1-3 hours whereby the diluted initial cannabis extract is decarboxylated to produce the refined, decarboxylated cannabis extract.
 12. A method of decarboxylation of cannabis extract comprising the steps of: adding a quantity of alcohol to an initial cannabis extract to produce a diluted solution; and refluxing the diluted solution at a temperature of about 180° C. for a period of about 1-3 hours. 